An understanding of the differential control of gene expression during the early development of higher organisms is most likely to come from detailed analysis of one of few genes which have dramatic experimental advantages over other experimental systems. One set of genes, the three yolk protein genes of Drosophila, have such advantages. They are non-repeated genes that are expressed in a tissue and time-specific manner under the control of hormonal stimulus. Moreover, they are in an organism that is particularly favorable for a combined molecular and biological analysis. I propose to use the genes which I and several colleagues have recently cloned and characterized, to examine the pattern of in vivo transcription. Through a combination of hybridization techniques, such as Southern and Northern transfer gels, Berk and Sharp (1977) nuclease analysis, and limited sequencing of the 3' and 5' ends of transcripts, I plan to determine the processing steps that convert the primary transcript products to the three mature mRNAs and to determine the timing of transcription. The possibility of amplification and co-transcription of these genes will also be investigated. The objective of these studies is to obtain a detailed description of the in vivo transcription of yolk protein genes during development, so that genetic and in vitro manipulation of these genes and their nearby sequences can lead to tests of developmental control models.